The invention relates to a method for the manufacture of panes with high transmissivity in the visible range of the spectrum and with high reflectivity for thermal radiation, by coating transparent substrates by cathode sputtering, and to panes manufactured by the method.
Such panes are intended, especially in winter, to prevent heat from being radiated away from a room to the outdoors. Suitable coating systems are generally referred to as "low-e" (low emissivity).
A low-e system of layers consists of various classes of coatings which have to have various properties and also to serve different purposes in this system:
a) In general, an electrically highly conductive layer, often a metal such as Ag, Au or Cu, with a very low emissivity coefficient, which is the actual low-e (low emissivity) coating. PA1 b) Since, however, a metal layer has a high reflectivity for light (i.e., a low transmission of light) in the visible range, it is dereflectivized by means of additional transparent coatings. Another purpose of these transparent coatings is to assure a desired shade of color and a high mechanical strength and chemical resistance in the system. PA1 c) In order to protect the thin metal layer against an aggressive ambient atmosphere both during the manufacturing process and after manufacture, and at the same time to assure good adherence of the next adjacent oxide coating, often a so-called blocking layer (barrier layer, adhesivizing layer) of metal or suboxide is applied to this metal layer. PA1 Substrate / Oxide / Silver / Blocker / Oxide.
In order to satisfy the above purposes, a low-e coating of the prior art has been built up as follows:
The substrate is a transparent, inorganic or organic glass sheet or a transparent, organic film.
The silver is an electrically conductive layer.
The oxides form the anti-reflective coating, and
The blocker forms the protective coating for the silver layer and the adhesivizer for the oxide layer.
All of the low-e coating systems known heretofore react very sensitively to moisture, especially at elevated temperature such as during the summer months. Under such conditions the silver layer agglomerates and oxidizes, and for this reason dark specks form on the coating system. The metal blockers or suboxide blockers of metals such as Al, Cu, Cr, Zr, Ti, Ni, Zn, Ta and others or their alloys evidently do not sufficiently protect the present low-e system against corrosion.
A higher resistance of the low-e coating to sodium chloride is especially necessary if the manufactured panes are to be transported overseas. High resistance to sulfur dioxide, on the other hand, is necessary if the pane is to be used, for example, in heavy industrial regions where very high atmospheric pollution by sulfur dioxide prevails.
The low-e coatings known heretofore are mechanically soft and their chemical stability, especially against moisture (e.g., aqueous salt or sodium dioxide solutions), is unsatisfactory. Experience has shown that some of the known coating systems (U.S. Pat. No. 4,413,877, DE 33 07 661, EP 0 158 318, EP 0 226 993, U.S. Pat. No. 4,786,563) are completely destroyed within two hours under test conditions which are defined in DIN 50021 (NaCl test) or DIN 50018 (SO.sub.2 test).
There are also low-e coating systems which do have satisfactory stability toward moisture (EP 0 304 234, U.S. Pat. No. 4,985,312). None of these coating systems, however, is sufficiently resistant to aqueous sodium chloride or aqueous sulfur dioxide (as established in standards DIN 50021 and DIN 50018).